Alien City is a Icehouse/piecepack hybrid game. To play, you will need a piecepack set and:

5 large red pyramids

5 large blue pyramids

4 large green pyramids

3 small red pyramids

3 small blue pyramids

The color of the large pyramids is important so that the pyramids interface with the piecepack graphics, but suitable adaptations can be made to accomodate other colors. The color of the small pyramids is arbitrary as long as they are distinct for each player.

You can also play with 2 Treehouse sets by using different sizes for each color. The size is not used by the game, so that doesn't change it. Instead of the small reds and blues, you can a tree pieces from the leftover colors (Black and Yellow).